The 3rd Generation Partnership Project (3GPP), which is a standardization project, standardized the Evolved Universal Terrestrial Radio Access (hereinafter referred to as EUTRA), in which high-speed communication is realized by adopting an orthogonal frequency-division multiplexing (OFDM) communication scheme and flexible scheduling using a unit of prescribed frequency and time called resource block.
Moreover, the 3GPP has been discussing Advanced EUTRA, which realizes higher-speed data transmission and has backward compatibility with EUTRA. EUTRA relates to a communication system based on a network in which base station devices have substantially the same cell configuration (cell size), but, regarding Advanced EUTRA, discussion has been made on a communication system based on a network (different-type radio network, heterogeneous network) in which base station devices (cells) having different configurations coexist in the same area.
Discussion has been made on a dual connectivity technique, in which, in a communication system where cells (macro cells) having large cell radii and cells (small cells) having smaller cell radii than those of the macro cells coexist as in a heterogeneous network, a terminal device performs communication by connecting to a macro cell and a small cell at the same time (NPL 1).
In NPL 1, discussion is advanced regarding a network based on a situation that, when a terminal device is to establish dual connectivity with a cell (macro cell) having a large cell radius (cell size) and a cell (small cell (or pico cell)) having a small cell radius, a backbone network (backhaul) between the macro cell and the small cell is slow, and a delay occurs. Specifically, there is a possibility that it is impossible or difficult to enable a function which has been enabled in prior scenarios, due to delay in exchange of control information or user information between the macro cell and the small cell.
Meanwhile, NPL 2 describes a method of, when a terminal device connects, at the same time, to a plurality of cells connected via a high-speed backhaul, feeding back channel state information of each cell.